Why are you even expecting your grand children to open presents early, even though you want to see them do it. Christmas presents are not opened before Christmas morning. End of.
I only see my DGC open their presents every other Christmas when they are with me. We visit every 'away' year just before Christmas to deliver the presents, but I would be horrified if it was suggested that they should be opened ahead of the Great Day just so we could see their pleasure.
Good Morning Thursday 5th November 2026
) and I've never thought it was a problem.